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Topic: How to promote controlled ringing with an op amp circuit (Read 2733 times) previous topic - next topic


A Sallen-Key active low pass filter worked well for me when I wanted that. Since we're still having fun.
  ... with a transistor and a large sum of money to spend ...
Please don't PM me with technical questions. Post them in the forum.


It must be the 5 minute rule. He only has 14 posts, you know. 8)
"The problem is in the code you didn't post."


This may come as a surprise but I don't know what the 5 minute rule is
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter


No technical PMs.
If you are asked a question, please respond with an answer.
If you are asked for more information, please supply it.
If you need clarification, ask for help.


Just as well.  The OP's post was worded like a homework assignment. Think about it. He says he "has a transducer.." . He doesn't say "I have THIS transducer [link] .  He doesn't say WHAT he doing. He doesn't say WHY he wants ringing. He says he wants to use an op amp but obviously does not know ANYTHING about op amps. Does not even know what a Voltage Follower is because he describes one to a T but not by name.  He describes an LPF but not by name.  Instead of saying " Can I use an op amp to generate such and such an output from a [ sensor name] input ?" he starts out by asking "what op amp configuration follows the voltage of it's input ?" (is that a trick question?)
Obviously he's never used an op amp.. He asks for an " under damped controlled system but doesn't know the first thing about Control Systems (like PID parameters for starters).
I am back now. Sorry that my question seems to have offended you so much! This was not a homework assignment, and thanks to the people who gave helpful answers my memory was jogged and I remembered the Sallen Key filter topology and I have now implemented this into a Spice model and the results are great!
My transducer (since you seem keen to know) is a microphone and pre-amplifier which I made myself, therefore there is no "link". And by the way I know what a "voltage follower" is.
What I was after was a low-pass-filter topology which would allow me to chose the components easily so that I can control the time reponse of the second order system. Hence allowing me to chose the overshoot, damping, settling time etc.
The Sallen Key transfer function allows me to select the resistances/capacitances so that I know what the response will be. Thanks to those that mentioned this. And by the way, anyone who possesses any real knowledge and experience should be happy to share it, not to mock and belittle others whilst reeling phrases like "he doesn't even know..." or "he has never heard of...".


May 20, 2016, 09:30 pm Last Edit: May 21, 2016, 11:47 am by raschemmel
Sorry about that. I was never offended.
You're right, I should have given you the benefit of the doubt

Why don't you show your work ?
( for the benefit of those who did help you)

Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter


Yea, but Hairbair, you've made a bunch of posts here,so you have probably read a bit as well. Surely you have noticed that questions like yours require more detailed information in order to be sufficiently answered. When someone posts a partial question, then disappears for a few days, a bit of humor at their expense is to be expected.
What, I need to say something else too?


This post is over 20 Replies and there is basically no schematic or anything that would be of any value to any other forum member. If you have solved your problem that prompted you to post on the forum, you owe it to all the people who tried to help you and all the other forum members to post your final schematic and any calculations you did to arrive at your solution. This is an open source forum. The concept is that helping one member helps everyone else because the information is shared, What did we get out of this post ? (aside from maybe I was unfairly harsh LOL)
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter


Hi all,
Thanks to all those who gave positive and helpful feedback
Attached is a circuit of what I wanted at the beginning and a simulation waveform.
In order to achieve the desired ringing frequency and Q factor the wikipedia site on Sallen Key topology is really helpful, it explains all the terms of the second order system and how they relate to the components:


Jul 28, 2016, 09:03 pm Last Edit: Jul 28, 2016, 11:16 pm by raschemmel
I would recommend the LT1215 op amp.
Also, from past experience building op amp active filters, I would recommend using high quality caps.

You last post, by itself , is no revelation. You have not posted any design criteria for the filter, like cutoff frequency.  

We have more free parameters than we really need so we can set R1=R2=R.
I believe the same is true for C1 and C2 (C1 = C2)

What is the cutoff frequency ?

I have a transducer that creates a step voltage (0 to 4.5V) with a proximity stimulus, However I would like to put this step input into an op amp where the output of the op amp will follow the step input but with a controlled amount of ringing (both amplitude and settling time). This is essentially a controlled under-damped system. 
Still no information on the transducer.
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter


Why are you set on an analog circuit to do this?  You can do this with a digital filter easily using an Arduino.


A Vien briidge with gain preset at < 3 would do it - but why would anyone want it ??



Easy to google if spelt right: Wien bridge oscillator.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

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